Radiographic image conversion panel, method for manufacturing the same, method for forming phosphor particle, method for forming photostimulable phosphor precursor, phosphor precursor and photostimulable phosphor

ABSTRACT

A radiographic image conversion panel includes: a support; and at least one photostimulable phosphor layer provided on the support, wherein at least one layer of the photostimulable phosphor layers contains a photostimulable phosphor using an alkali halide represented by a general formula.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional application under 35 U.S.C. §120of U.S. patent application Ser. No. 10/719,919, filed on Nov. 21, 2003,the entire contents of which are incorporated herein by reference. TheSer. No. 10/719,919 application claimed the benefit under 35 U.S.C. §119of the dates of the earlier filed Japanese Patent Application Nos. JP2002-343432 filed Nov. 27, 2002 and JP 2003-079233 filed Mar. 24, 2003,priority to which is also claimed herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiographic image conversion panel,a method for manufacturing the radiographic image conversion panel, amethod for forming phosphor particles, a method for forming aphotostimulable phosphor precursor, a phosphor precursor and aphotostimulable phosphor.

2. Description of Related Art

In earlier technology, so-called radiography in which a silver salt isused in order to obtain a radiographic image has been utilized. However,a method for imaging a radiological image without using a silver salthas been developed. That is, a method for imaging by absorbing aradiation ray transmitted through a subject in a phosphor, thereafter,exciting the phosphor with a certain type of energy, and radiating theradiographic energy accumulated in the phosphor as a fluorescence isdisclosed.

Concretely, a radiographic image conversion method in which a panelprovided with a photostimulable phosphor layer on a support and eitheror both of visible ray and infrared ray is used as excitation energy hasbeen known (see U.S. Pat. No. 3,859,527 specification).

As radiographic image conversion methods using photostimulable phosphorshaving higher luminance and higher sensitivity, a radiographic imageconversion method using a BaFX:Eu²⁺ system (X: Cl, Br, I) phosphor (forexample, see Japanese Patent Laid-Open Publication No. Sho 59-75200), aradiographic image conversion method using an alkali halide phosphor(for example, see Japanese Patent Laid-Open Publication No. Sho61-72087), and an alkali halide phosphor containing metals of Tl⁺, Ce³⁺,Sm³⁺, Eu³⁺, Y³⁺, Ag⁺, Mg²⁺, Pb²⁺, In³⁺ as co-activators (for example,see Japanese Patent Laid-Open Publications Nos. Sho 61-73786 and Sho61-73787) are developed.

Furthermore, recently, in analysis of diagnostic imaging, a radiographicimage conversion panel having higher sharpness has been required. As amethod for improving the sharpness, for example, attempts for improvingsensitivity and sharpness by controlling the shape of photostimulablephosphors (hereinafter, also referred to as phosphors) have been made.

As one of these attempts, for example, there is a method for using aphotostimulable phosphor layer having a fine quasi-columnar block formedby depositing a photostimulable phosphor on a support having a fineconcavoconvex pattern (for example, see Japanese Patent Laid-OpenPublication No. Sho 61-142497).

Further, a method for using a radiographic image conversion panel havinga photostimulable phosphor layer in which cracks between columnar blocksobtained by depositing a photostimulable phosphor on a support having afine pattern are shock-treated to be further developed (for example, seeJapanese Patent Laid-Open Publication No. Sho 61-142500), further, amethod for using a quasi-columnar radiographic image conversion panel inwhich cracks are caused from the surface side of a photostimulablephosphor layer formed on a support (for example, see Japanese PatentLaid-Open Publication No. Sho 62-39737), furthermore, a method forproviding cracks by forming a photostimulable phosphor layer having avoid on a support according to deposition, and thereafter, by growingthe void according to heat treatment (for example, see Japanese PatentLaid-Open Publication No. Sho 62-110200), and the like are suggested.

Furthermore, a radiographic image conversion panel having aphotostimulable phosphor layer in which an elongated columnar crystalhaving a constant slope to a normal line direction of a support isformed on the support according to a vapor phase deposition method (forexample, see Japanese Patent Laid-Open Publication No. Hei 2-58000) issuggested.

Any of these processes of controlling shapes of the photostimulablephosphor layer is characterized in that since the transversal diffusionof stimulating excitation light or stimulated fluorescence can besuppressed by rendering the photostimulable phosphor layer columnar (thelight reaches the support surface while repeating reflection in a crack(columnar crystal) interface), the sharpness of images formed by thestimulated fluorescence can be noticeably increased.

Recently, a radiographic image conversion panel using a photostimulablephosphor in which Eu is activated to a ground material of alkali halidesuch as CsBr or the like is suggested. Particularly, it became possibleto derive a high X-ray conversion efficiency, which was unable to beobtained in earlier technology, by using Eu as an activator.

However, diffusion of Eu according to heat is remarkable, and there is aproblem such that the dispersion of Eu is easily caused and theexistence of Eu in a ground material is distributed unevenly since thevapor pressure under vacuum is also high. Thereby, it has not yet beenin practical use at market since it is difficult to activate it by usingEu and to obtain a high X-ray conversion efficiency.

Particularly, in activation of rare-earth element which is excellent ina high X-ray conversion efficiency, with respect to deposited filmformation under vacuum, uniformizing is more difficult problem thanvapor pressure property. Further, in manufacturing method, there is aproblem such that the existence state of the activator becomesnonuniform since a number of heat treatments, such as heating of rawmaterials when preparing the photostimulable phosphor layers, heating ofsubstrates (supports) at the time of vacuum deposition, and anneling(strain relaxation of substrates (supports)) treatment after filmformation, is performed to these photostimulable phosphor layers formedby vapor phase growth (deposition). Further, there is a problem relatingto the durability thereof.

Therefore, there have been demanded improvements in luminance, sharpnessand durability which are demanded from a market as the radiographicimage conversion panel.

On the other hand, particularly, in activation by a rare earth elementwhich ensures high X-ray conversion efficiency, when forming a vapordeposition film in a vacuum, the heating during the vapor depositiongenerates a radiation heat on a substrate to exert an effect on a heatdistribution of the substrate.

This heat distribution varies also depending on a degree of vacuum, andthe crystal growth becomes uneven by the heat distribution to cause arapid disturbance in the luminance and the sharpness, so that it isdifficult to control these performances in the vacuum deposition filmformation method.

When using a phosphor crystal prepared by using an alkali halide as theground material, the performance as a phosphor is brought out by asingle crystal forming method according to a vapor phase depositionmethod (a vacuum deposition method) or a pull method, and the phosphorcrystal is sealed in a glass or metal case due to low moistureresistance thereof.

In the CsBr:Eu phosphor radiographic image conversion panel manufacturedby using a vacuum deposition method, there are problems that the Eucannot be stably diffused in a vacuum conditions at the formationdescribed above and that the phosphor has a large limitation on thehandling because it is sealed in a glass case due to low moistureresistance thereof and therefore, has difficulties in use for generalpurposes.

However, Eu has properties that diffusion by heat is remarkable and alsothe vapor pressure in a vacuum is high, so that there arises a problemthat Eu is unevenly distributed in a ground material because it iseasily dispersed in the ground material. Accordingly, it is difficult toactivate a phosphor using Eu to attain high X-ray conversion efficiencyand therefore, the method is not put into practical use on a market.

In the rare earth element activator which ensures high X-ray conversionefficiency, when employing the vacuum deposition film forming method,the heating during the vapor deposition generates a radiation heat on asubstrate to exert an effect on a heat distribution of the substrate.

This heat distribution varies also depending on a degree of vacuum, andthe crystal growth becomes uneven by the heat distribution to cause arapid disturbance in the luminance and the sharpness, so that it isdifficult to control these performances in the vacuum deposition filmforming method (e.g., see Japanese Patent Laid-Open Publication No.H10-140148 and Japanese Patent Laid-Open Publication No. H10-265774).Accordingly, the vacuum deposition film forming method has problems inthat, particularly, in the case of using the rare earth elements such asEu, Eu cannot be stably diffused and the phosphor has a large limitationon the handling because it is sealed in a glass case due to low moistureresistance thereof. Further, the method is lacking in versatilitybecause the raw material utilization efficiency is as low as onlyseveral % to 10%, resulting in high cost due to the low utilizationefficiency.

Accordingly, in the market, there have been demanded improvements inproduction uniformity agreeing with the improvements of stability,luminance and sharpness which are required as a radiographic imageconversion panel.

SUMMARY OF THE INVENTION

An embodiment of the present invention is to provide a radiographicimage conversion panel having high luminance, high sharpness andexcellent durability, and to provide a manufacturing method of theradiographic image conversion panel.

Further, another embodiment of the invention is to provide aradiographic image conversion panel which is excellent in uniformity ofan activator in a phosphor layer and which exhibits high luminance andhigh sharpness, and to provide a method for manufacturing theradiographic image conversion panel.

In order to accomplish the above-mentioned embodiment, in accordancewith the first aspect of the present invention, a radiographic imageconversion panel comprises:

a support; and

at least one photostimulable phosphor layer provided on the support,

wherein at least one layer of the photostimulable phosphor layers isformed by a photostimulable phosphor represented by a following generalformula (1), and

an amount of activation metal atoms at an end of a photostimulablephosphor crystal and an amount of activation metal atoms in the vicinityof the support satisfy a following formula 1:0≦(the amount of the activation metal atoms at the end of thephotostimulable phosphor crystal)/(the amount of the activation metalatoms in the vicinity of the support)<1, and

the general formula (1) is expressed byM ¹ X·aM ² X′ ₂ ·bM ³ X″ ₃ :eA  (1)

wherein the M¹ is at least one kind of alkali metal selected from agroup consisting of Li, Na, K, Rb and Cs, the M² is at least one kind ofbivalent metal atom selected from a group consisting of Be, Mg, Ca, Sr,Ba, Zn, Cd, Cu and Ni, the M³ is at least one kind of trivalent metalatom selected from a group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga and In, each of the X, the X′and the X″ is at least one kind of halogen selected from a groupconsisting of F, Cl, Br and I, the A is at least one kind of metal atomselected from a group consisting of Eu, Tb, In, Ce, Tm, Dy, Pr, Ho, Nd,Yb, Er, Gd, Lu, Sm, Y, Tl, Na, Ag, Cu and Mg and each of the a, the band the e represents a numeric value in a range of 0≦a<0.5, 0≦b<0.5 and0<e≦0.2.

In accordance with the second aspect of the present invention, aradiographic image conversion panel comprises:

a support; and

at least one photostimulable phosphor layer provided on the support,

wherein at least one layer of the photostimulable phosphor layerscontains a photostimulable phosphor using an alkali halide representedby a following general formula (1) as a ground material, and

the photostimulable phosphor layer is formed so as to have a thicknessfrom 50 μm to 20 mm by a vapor phase growth method (also referred to as“vapor phase deposition method”, and a mean crystal size in thephotostimulable phosphor of the photostimulable phosphor layer is from90 to 1000 nm, and

the general formula (1) is expressed byM ¹ X·aM ² X′ ₂ ·bM ³ X″ ₃ :eA  (1)

wherein the M¹ is at least one kind of alkali metal selected from agroup consisting of Li, Na, K, Rb and Cs, the M² is at least one kind ofbivalent metal atom selected from a group consisting of Be, Mg, Ca, Sr,Ba, Zn, Cd, Cu and Ni, the M³ is at least one kind of trivalent metalatom selected from a group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga and In, each of the X, the X′and the X″ is at least one kind of halogen selected from a groupconsisting of F, Cl, Br and I, the A is at least one kind of metal atomselected from a group consisting of Eu, Tb, In, Ce, Tm, Dy, Pr, Ho, Nd,Yb, Er, Gd, Lu, Sm, Y, Tl, Na, Ag, Cu and Mg and each of the a, the band the e represents a numeric value in a range of 0≦a<0.5, 0≦b<0.5 and0<e≦0.2.

The photostimulable phosphor may be CsBr:Eu.

In accordance with the third aspect of the present invention, a methodfor manufacturing the above radiographic image conversion panel,comprises controlling a deposition rate of a main agent of thephotostimulable phosphor and a deposition rate of an activator of thephotostimulable phosphor by at least two or more systems.

In accordance with the fourth aspect of the present invention, a methodfor manufacturing a radiographic image conversion panel comprises asupport and a photostimulable phosphor layer provided on the support;the method comprising adding Rb atoms to a photostimulable phosphor ofthe photostimulable phosphor layer so that a ratio of the Rb atoms to Csatoms is 1/1,000,000 to 5/1,000 mol.

In accordance with the fifth aspect of the present invention, aradiographic image conversion panel comprises a photostimulable phosphorobtained by the method for manufacturing the above radiographic imageconversion panel, wherein in the photostimulable phosphor, a main peakis shown from a (400) face in accordance with a result of X-raydiffraction.

The radiographic image conversion panel may comprise: a photostimulablephosphor layer,

wherein the photostimulable phosphor layers contains the photostimulablephosphor using an alkali halide represented by a following generalformula (1) as a ground material,

the photostimulable phosphor layer is formed by spherical phosphorparticles and a polymer material,

the photostimulable phosphor layer is formed so as to have a thicknessfrom 50 μm to 20 mm,

the general formula (1) is expressed byM ¹ X·aM ² X′ ₂ ·bM ³ X″ ₃ :eA  (1)

wherein the M¹ is at least one kind of alkali metal selected from agroup consisting of Li, Na, K, Rb and Cs, the M² is at least one kind ofbivalent metal atom selected from a group consisting of Be, Mg, Ca, Sr,Ba, Zn, Cd, Cu and Ni, the M³ is at least one kind of trivalent metalatom selected from a group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga and In, each of the X, the X′and the X″ is at least one kind of halogen selected from a groupconsisting of F, Cl, Br and I, the A is at least one kind of metal atomselected from a group consisting of Eu, Tb, In, Ce, Tm, Dy, Pr, Ho, Nd,Yb, Er, Gd, Lu, Sm, Y, Tl, Na, Ag, Cu and Mg and each of the a, the band the e represents a numeric value in a range of 0≦a<0.5, 0≦b<0.5 and0<e≦0.2.

Preferably, phosphor fine particles in the photostimulable phosphor areformed by heating at 400° C. or more.

In accordance with the sixth aspect of the present invention, in aphotostimulable phosphor precursor, phosphor particles in the aboveradiographic image conversion panel are formed in a vacuum.

In accordance with the seventh aspect of the present invention, a methodfor forming the above photostimulable phosphor precursor, comprises:

sequentially forming a liquid membrane phase in a liquid phasecontaining Cs atoms, and adding an organic solvent having a solubilitydifferent from that of the liquid phase containing Cs atoms understirring.

In accordance with the eighth aspect of the present invention, aphotostimulable phosphor obtained by calcining the above phosphorprecursor at 600 to 800° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below and the accompanying drawingwhich are given by way of illustration only, and thus are not intendedas a definition of the limits of the present invention, and wherein;

FIG. 1 is a cross-sectional view showing one example of thephotostimulable phosphor layer having a columnar crystal formed on thesupport;

FIG. 2 is a view showing a state where the photostimulable phosphorlayer is formed on the support by a vapor deposition method;

FIG. 3 is a schematic view showing one example of the construction ofthe radiographic image conversion panel according to the presentinvention; and

FIG. 4 is a schematic view showing one example of the method forpreparing the photostimulable phosphor layer on the support by vapordeposition.

PREFERRED EMBODIMENTS OF THE INVENTION

Hereinafter, the present invention will be described in detail below.

First Embodiment

In the first embodiment of the radiographic image conversion panelaccording to the present invention, the radiographic image conversionpanel comprises a support, and at least one photostimulable phosphorlayer provided on the support, wherein at least one layer of thephotostimulable phosphor layers is formed by the photostimulablephosphor represented by the general formula (1) described below, and theamount of the activation metal atoms (activator: Eu) at the front end ofthe photostimulable phosphor crystals and the amount of the activationmetal atoms (activator: Eu) in the vicinity of the support satisfy thefollowing formula (1).0≦(the amount of the activation metal atoms at the front end ofphotostimulable phosphor crystals)/(the amount of Eu in the vicinity ofthe support)<1  Formula (1)

Measuring Method of the Amount of Eu

A part corresponding to 20% of the total length in a thickness directionof the vapor deposition film crystal is taken out from the front end ofthe crystal and designated as the part of the front end of the crystal.

A part corresponding to 20% of the total length in a thickness directionof the vapor deposition film crystal is taken out from the support sideand designated as the support side of the crystal.

As for the takeout, the part may be mechanically cut out by a spatulaand the like, or may be cut out by performing an ion beam machining suchas FIB.

The powder cut out is dissolved in water and the amount of Eu can beanalyzed and measured by using ICP.

The crystal cut out can be measured on the amount of Eu by usingTOF-SIMS.

Next, the photostimulable phosphor represented by the general formula(1), which is preferably used in the present invention, will beexplained.

General Formula (1)M ¹ X·aM ² X′ ₂ ·bM ³ X″ ₃ :eA  (1)

wherein the M¹ is at least one kind of alkali metal selected from agroup consisting of Li, Na, K, Rb and Cs, the M² is at least one kind ofbivalent metal atom selected from a group consisting of Be, Mg, Ca, Sr,Ba, Zn, Cd, Cu and Ni, the M³ is at least one kind of trivalent metalatom selected from a group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga and In, each of the X, the X′and the X″ is at least one kind of halogen selected from a groupconsisting of F, Cl, Br and I, the A is at least one kind of metal atomselected from a group consisting of Eu, Tb, In, Ce, Tm, Dy, Pr, Ho, Nd,Yb, Er, Gd, Lu, Sm, Y, Tl, Na, Ag, Cu and Mg and each of the a, the band the e represents a numeric value in a range of 0≦a<0.5, 0≦b<0.5 and0<e≦0.2.

In the photostimulable phosphor represented by the general formula (1),M¹ represents at least one alkali metal atom selected from a groupconsisting of Li, Na, K, Rb and Cs. Among these, at least one alkaliearth metal atom is preferably selected from a group consisting of Rband Cs, and Cs atom is more preferable.

M² represents at least one divalent metal atom selected from a groupconsisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu and Ni. Among these, adivalent metal atom selected from a group consisting of Be, Mg, Ca, Srand Ba is preferably used.

M³ represents at least one trivalent metal atom selected from a groupconsisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,Yb, Lu, Al, Ga and In. Among these, a trivalent metal atom selected froma group consisting of Y, Ce, Sm, Eu, Al, La, Gd, Lu, Ga and In ispreferably used.

A is at least one metal atom selected from a group consisting of Eu, Tb,In, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, Tl, Na, Ag, Cu andMg.

From the viewpoint of the improvement in stimulated emission luminanceof the photostimulable phosphor, X, X′ and X″ each represents at leastone halogen atom selected from a group consisting of F, Cl, Br and I.Preferred is at least one halogen atom selected from a group consistingof F, Cl and Br, and more preferred is at least one halogen atomselected from a group consisting of Br and I.

In the compound represented by the general formula (1), a is a numberwithin the range of 0≦a<0.5, preferably 0≦a<0.01; b is a number withinthe range of 0≦b<0.5, preferably 0≦b≦10⁻²; and e is a number within therange of 0<e≦0.2, preferably 0<e≦0.1.

The photostimulable phosphor represented by the general formula (1) isprepared, for example, by a preparation method described below.

First, as phosphor raw materials, the following crystal is prepared byadding an acid (HI, HBr, HCl or HF) to a carbonate and mixing understirring. Then, the mixture is filtered at a point of neutralization toobtain a filtrate. The water content of the filtrate is vaporized toobtain the following composition.

As the phosphor raw materials, there may be employed:

(a) at least one compound selected from NaF, NaCl, NaBr, NaI, KF, KCl,KBr, KI, RbF, RbCl, RbBr, RbI, CsF, CsCl, CsBr and CsI;

(b) at least one compound selected from MgF₂, MgCl₂, MgBr₂, MgI₂, CaF₂,CaCl₂, CaBr₂, CaI₂, SrF₂, SrCl₂, SrBr₂, SrI₂, BaF₂, BaCl₂, BaBr₂,BaBr₂.2H₂O, BaI₂, ZnF₂, ZnCl₂, ZnBr₂, ZnI₂, CdF₂, CdCl₂, CdBr₂, CdI₂,CuF₂, CuCl₂, CuBr₂, CuI, NiF₂, NiCl₂, NiBr₂ and NiI₂; and

(c) a compound having a metal atom selected from a group consisting ofEu, Tb, In, Cs, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, Tl, Na,Ag, Cu and Mg.

The phosphor raw materials of the above-described (a)-(c) are weighed soas to form a mixture composition within the above-described numberrange, and dissolved in purified water.

At this time, the materials may be thoroughly mixed by use of a mortar,a ball mill, a mixer mill, etc.

Next, to the aqueous solution obtained, a predetermined acid is added sothat a pH value C of the solution is adjusted to 0<C<7, then, the watercontent is evaporated from the solution.

Next, the raw material mixture obtained is filled in a heat-resistingvessel such as a quartz crucible or an alumina crucible, and calcinationis conducted in an electric furnace. The calcination temperature may bepreferably from 500 to 1000° C. The calcination time, which may differdepending on the filled amount of the raw material mixture, thecalcination temperature, etc., may be preferably from 0.5 to 6 hours.

The calcination atmosphere may be preferably a weak reducing atmospheresuch as a nitrogen gas atmosphere containing a small amount of hydrogengas and a carbon dioxide atmosphere containing a small amount of carbonmonoxide, a neutral atmosphere such as a nitrogen gas atmosphere and anargon gas atmosphere, or a weak oxidizing atmosphere containing a smallamount of oxygen gas.

Further, if the mixture is once calcined under the above calcinationconditions, the calcined product is then taken out from the electricfurnace for pulverization, and then the calcined product powder is againfilled in a heat-resisting vessel and placed in the electric furnace tocarry out re-calcination under the same calcination conditions asdescribed above, the emission luminance of phosphors can be furtherenhanced. Also, during cooling of the calcined product from thecalcination temperature to a room temperature, if the calcined productis taken out from the electric furnace and left to cool in an air, adesired phosphor can be obtained, or the product may be cooled in thesame weak reducing atmosphere or neutral atmosphere as that during thecalcination. Also, if the calcined product is cooled quickly in a weakreducing atmosphere, a neutral atmosphere or a weak oxidizing atmosphereby moving it from the heating section to the cooling section in theelectric furnace, the stimulated emission luminescence of phosphorsobtained can be further enhanced.

In the above-described photostimulable phosphors, photostimulablephosphor particles containing iodine are preferable. For example,iodine-containing bivalent europium activated alkali earth metalfluorohalide phosphors, iodine-containing bivalent europium activatedalkali earth metal halide phosphors, iodine-containing rare earthelement activated rare earth oxyhalide phosphors, and iodine-containingbismuth activated alkali metal halide phosphors are preferable becausethese phosphors exhibit high luminance stimulated fluorescence, and aparticularly preferable photostimulable phosphor is an Eu added BaFIcompound.

Further, the photostimulable phosphor layer of the present invention isformed by a vapor phase growth method.

As the vapor phase growth method of the photostimulable phosphor, avapor deposition method, a sputtering method, a CVD method, an ionplating method, or the like can be used.

In the present invention, for example, the following methods can beused.

In the first vapor deposition method, a support is first placed in avapor deposition apparatus and the apparatus is then degassed to adegree of vacuum of about 1.333×10⁻⁴ Pa.

Then, at least one of the photostimulable phosphors is heated andevaporated by the resistance heating method, the electron beam method,etc. to have the photostimulable phosphor with a desired thickness grownon the support surface.

As a result, a photostimulable phosphor layer containing no binder isformed; it is also possible to form the photostimulable phosphor layerin a plurality of repetitions of the vapor deposition step.

In the vapor deposition step, it is also possible to have thephotostimulable phosphors co-vaporized using a plurality of resistiveheaters or electron beams in order to synthesize the intendedphotostimulable phosphor on the support and form the photostimulablephosphor layer concurrently.

After completion of vapor deposition, the photostimulable phosphor layeris provided with a protective layer on its side opposite to the supportside if necessary, to manufacture the radiographic image conversionpanel of the present invention. Alternatively, it is allowed to have thephotostimulable phosphor layer formed on a protective layer first, andthen to provide it with a support.

In the vapor deposition method, it is also allowed to cool or heat thelayer to be deposited onto the member to be deposited (the support, theprotective layer or the intermediate layer) during vapor deposition ifnecessary.

In addition, it is allowed to heat-treat the photostimulable phosphorlayer after the completion of vapor deposition. In the vapor depositionmethod, it is also allowed to perform the reactive vapor deposition ofdepositing the phosphors while introducing a gas such as O₂ or H₂ ifnecessary.

In the second sputtering method, a support having thereon a protectivelayer or an intermediate layer is placed in a sputtering apparatussimilarly to the vapor deposition method, then the apparatus is oncedegassed to a degree of vacuum of about 1.333×10⁻⁴ Pa, and subsequentlysuch an inert gas as Ar or Ne is introduced, as a sputtering gas, intothe sputtering apparatus to raise the gas pressure up to about1.333×10⁻¹ Pa. And then the photostimulable phosphor as a target issputtered to have a layer of the stimulated phosphor with a desiredthickness grown on the support.

In the sputtering step, various application processes can be usedsimilarly to the vapor deposition method.

As the third method, there is a CVD method. As the fourth method, thereis an ion plating method.

Further, a growth rate of the photostimulable phosphor layer in thevapor phase growth method is preferably from 0.05 to 300 μm/min. Whenthe growth rate is less than 0.05 μm/min., productivity of theradiographic image conversion panel of the present invention is poor andthis is not preferred. When the growth rate is in excess of 300 μm/min.,control of the growth rate is difficult and this is also not preferred.

In the case of obtaining the radiographic image conversion panel by thevacuum deposition method, the sputtering method, etc., since a binder isnot present, a packing density of the photostimulable phosphor can beincreased, so that the radiographic image conversion panel obtained ispreferable in terms of sensitivity and resolving power.

Further, the radiographic image conversion panel of the first embodimentis preferably manufactured by the binary vapor deposition method in thevapor phase growing methods. The binary vapor deposition method isdescribed below by referring to the phosphor CsBr:Eu.

In the present invention, when preparing a photostimulable phosphorlayer by a vapor phase method, the main agent deposition rate andactivator deposition rate in the photostimulable phosphor is controlledby at least two or more systems, for example, a binary vapor depositionmethod for separately depositing an Eu (activator) source and a CsBr(main agent) source is applied.

The object of the binary vapor deposition method in the presentinvention is to control the obtained deposition crystallinity, forexample, by controlling the amount of Eu incorporated into crystals, asa result, the radiographic image conversion panel having excellentluminance, sharpness and durability can be obtained.

In the binary vapor deposition method, for example, the Eu introductionmethod include a case of using two evaporation sources having differentconcentrations of CsBr:Eu, a case of using two evaporation sources ofCsBr element (main agent) and Eu element (activator) and a case of usingtwo evaporation sources of CsBr:Eu element (main agent) and Eu element(activator).

In any case, the amount of Eu (activator) introduced can be controlledby controlling the Eu (activator) introduction by the use of at leasttwo or more systems. The upper limit of the system is 100 systems orless.

The amount of Eu (activator) is as small as from 1/10,000 to 1/100 toCsBr as a main agent and therefore, when the film-forming rate of aphosphor film is decreased, the volatile amount is extremely reduced toresult in difficulty of the film formation. For attaining the filmformation, it is advantageous to increase the film-forming rate,however, when the film-forming rate is extremely increased, aconcentration distribution of Eu becomes uneven due to fluctuation atthe vapor deposition.

The deposition rate of the main agent and the activator is preferablyfrom 1 to 100 μm/min.

In order to solve this problem, boats at the binary vapor deposition arepreferably fixed twice or more for the Eu evaporation source.

The size of the boat is preferably from 1:2 to 1:10 due to limitation inan arrangement of a deposition apparatus.

In order to evaporate Eu, a resistance heating source disposed in thedeposition apparatus is disposed on Eu so as to form a film through aslit, and this is preferable in terms of further exerting an effect ofthe present invention. In addition, the slit is effective in preventingbumping of Eu.

That is, for improving the crystallinity in the outermost surface layerside of the phosphor, the concentration of Eu is decreased to form acrystal having excellent crystallinity and high transparency.

In the present invention, a rare earth Eu is preferably incorporatedinto the phosphor raw materials in an amount of from 1 to 100 times theEu amount to be introduced into the deposition film.

Further, a mean crystal size of the phosphor in the photostimulablephosphor layer of the present invention is preferably from 90 to 1000nm.

A film thickness of the photostimulable phosphor layer varies dependingon the intended use of the radiographic image conversion panel and thetype of the photostimulable phosphor, however, it is in the range of 50μm to 20 mm, preferably 50 μm to 1 mm, more preferably in the range of50 to 300 μm, further more preferably in the range of 100 to 300 μm,still more preferably in the range of 150 to 300 μm from the viewpointof obtaining the effect of the present invention.

In preparing the photostimulable phosphor layer according to the vaporphase growth method, a temperature of the support where thephotostimulable phosphor layer is formed is preferably set to 100° C. ormore, more preferably 150° C. or more, still more preferably 150 to 400°C.

Further, the photostimulable phosphor layer of the present inventionpreferably has a light reflective index of 20% or more, more preferably30% or more, still more preferably 40% or more, from the viewpoint ofobtaining the radiographic image conversion panel exhibiting highsharpness. Here, the upper limit is 100%.

Further, a filler such as a binder may be filled in a gap between thecolumnar crystals, whereby the photostimulable phosphor layer isreinforced. In addition, a substance having high percent absorption orhigh reflectance of light may be filled, whereby not only a reinforcingeffect is produced on the photostimulable phosphor layer but also thetransversal diffusion of the stimulating excitation light that enteredthe photostimulable phosphor layer can be effectively reduced.

Next, the construction of the photostimulable phosphor layer of thepresent invention is described by referring to FIGS. 1 and 2.

FIG. 1 is a schematic cross-sectional view showing one example of thephotostimulable phosphor layer having a columnar crystal formed on thesupport by using the above-described vapor phase growth method. Thereference numeral 11 denotes a support, 12 denotes a photostimulablephosphor layer, and 13 denotes a columnar crystal constructing thephotostimulable phosphor layer. Incidentally, 14 denotes a gap formedbetween the columnar crystals.

FIG. 2 is a view showing a state where the photostimulable phosphorlayer is formed on the support by the vapor deposition. When an incidentangle of a photostimulable phosphor steam flow 16 to the normal linedirection (R) of the support surface is θ₂ (in FIG. 2, the steam flowenters at an angle of 60 degrees), an angle of the formed columnarcrystal to the normal line direction (R) of the support surface isrepresented by θ₁ (in FIG. 2, it is about 30 degrees, and experientiallyit is about half of the incident angle) and the columnar crystal isformed at this angle.

The photostimulable phosphor layer thus formed on the support hasexcellent directivity because of the absence of binder therein andtherefore, it has high directivity of stimulating excitation light andstimulated fluorescence, so that the layer can be increased in thethickness than the radiographic image conversion panel having adispersed-type photostimulable phosphor layer containing aphotostimulable phosphor dispersed in a binder. Further, the scatteringof stimulating excitation light in the photostimulable phosphor layerdecreases to result in improvement in the sharpness of images.

Further, a filler such as a binder may be filled in a gap between thecolumnar crystals, whereby the photostimulable phosphor layer isreinforced. In addition, a substance having high percent absorption orhigh reflectance of light may be filled, whereby not only a reinforcingeffect is produced on the photostimulable phosphor layer but also thetransversal diffusion of the stimulating excitation light that enteredthe photostimulable phosphor layer can be effectively reduced.

The substance having high reflectance of light means a substance havinghigh reflectance for stimulating excitation light (500-900 nm,specifically 600-800 nm). For example, there may be used aluminum,magnesium, silver, indium, and other metals, a white pigment and a greenor red coloring material. The white pigment can reflect also lightemitted from a stimulated fluorescence.

Examples of the white pigments include TiO₂ (anatase type, rutile type),MgO, PbCO₃.Pb(OH)₂, BaSO₄, Al₂O₃, M_((II))FX (provided that M_((II)) isat least one atom selected from a group consisting of Ba, Sr and Ca; Xis a Cl atom or a Br atom), CaCO₃, ZnO, Sb₂O₃, SiO₂, ZrO₂, lithopone(BaSO₄.ZnS), magnesium silicate, basic lead siliconsulfate, basic leadphosphate, and aluminum silicate.

Since these white pigments have a strong hiding power and greatrefractive index, they easily scatter stimulated fluorescence byreflection or refraction of light, thus permitting noticeableimprovement of the sensitivity of the obtained radiographic imageconversion panel.

Examples of the substances of high absorption include carbon black,chromium oxide, nickel oxide, and iron oxide; and a blue coloringmaterial. Of these substances, carbon black absorbs also light emittedfrom a photostimulable phosphor.

As the coloring material, any organic or inorganic coloring material canbe used.

Examples of the organic coloring materials include Zapon Fast Blue 3G(produced by Hoechst), Estrol Brill Blue N-3RL (produced by SumitomoChemical Co., Ltd.), D & C Blue No. 1 (produced by National Aniline),Spirit Blue (produced by Hodogaya Chemical Co., Ltd.), Oil Blue No. 603(produced by Orient Chemical Industries Co., Ltd.), Kiton Blue A(produced by Chiba-Geigy), Aizen Catiron Blue GLH (produced by HodogayaChemical Co., Ltd.), Lake Blue AFH (produced by Kyowa Sangyo),Primocyanine 6GX (produced by Inabata & Co., Ltd.), Brill Acid Green 6BH(produced by Hodogaya Chemical Co., Ltd.), Cyan Blue BNRCS (produced byToyo Ink Mfg. Co., Ltd.), and Lionoil Blue SL (produced by Toyo Ink Mfg.Co., Ltd.).

Mention may also be made of organic metal complex salt coloringmaterials such as Color Index Nos. 24411, 23160, 74180, 74200, 22800,23154, 23155, 24401, 14830, 15050, 15760, 15707, 17941, 74220, 13425,13361, 13420, 11836, 74140, 74380, 74350, and 74460.

Examples of the inorganic coloring materials include inorganic pigmentssuch as ultramarine, cobalt blue, cerulean blue, chromium oxide, andTiO₂—ZnO—Co—NiO.

As the support to be used for the radiographic image conversion panel ofthe present invention, various kinds of glasses, for example, polymermaterials, metals, etc. may be employed. Preferred examples of thesupport include sheet glasses such as quartz glass, borosilicate glassand chemically reinforced glass; plastic films such as cellulose acetatefilm, polyester film, polyethylene terephthalate film, polyamide film,polyimide film, triacetate film and polycarbonate film; metal sheetssuch as aluminum sheet, iron sheet and copper sheet; or metal sheetshaving coated layers of the metal oxides.

Namely, the surface of these supports may be smooth, or may be matted toimprove adhesiveness with the photostimulable phosphor layer.

Further, in the present invention, an adhesive layer may also bepreviously provided on the surface of the support, if necessary, for theenhancement of adhesiveness between the support and the photostimulablephosphor layer.

The layer thickness of these supports may vary depending on the materialor the like of the supports to be used, but may generally range from 80to 2000 μm, more preferably from 80 to 1000 μm from the viewpoint ofhandling.

Instead of the forming of the adhesive layer, application liquidincluding the photostimulable phosphor and a predetermined binder as aphotostimulable phosphor layer, may be applied to the surface of thesupport. Alternatively, after the application liquid is applied to thesurface of the support, the photostimulable phosphor layer may be bound.

Representative examples of the binders which is included in theapplication liquid, include proteins such as gelatin, polysaccharidesuch as dextran, natural polymeric materials such as arabic gum andsynthetic polymeric materials such as polyvinyl butyral, polyvinylacetate, nitrocellulose, ethylcellulose, vinylidene chloride-vinylchloride copolymer, polyalkyl (metha)acrylate, vinylchloride-vinylacetate copolymer, polyurethane, cellulose acetatebutylate, polyvinyl alcohol and linear polyester. However, the presentinvention is characterized in that the binder is a resin mainly composedof a thermoplastic elastomer. Examples of the thermoplastic elastomerinclude the above-described polystyrene thermoplastic elastomer,polyolefin thermoplastic elastomer, polyurethane thermoplasticelastomer, polyester thermoplastic elastomer, polyamide thermoplasticelastomer, polybutadiene thermoplastic elastomer, ethylene-vinyl acetatethermoplastic elastomer, polyvinyl chloride thermoplastic elastomer,natural rubber thermoplastic elastomer, fluorine rubber thermoplasticelastomer, polyisoprene thermoplastic elastomer, chlorinatedpolyethylene thermoplastic elastomer, styrene-butadiene rubber andsilicone rubber thermoplastic elastomer.

Among these, a polyurethane thermoplastic elastomer and a polyesterthermoplastic elastomer are preferable because dispersibility isexcellent due to high bonding strength between the elastomer and thephosphor, and ductility is also excellent to improve bending resistanceof a radiation intensifying screen. In addition, these binders may becured with a cross linking agent.

A mixing ratio of the binder and the photostimulable phosphor in theapplication liquid varies depending on the set value of a haze degree ofthe objective radiographic image conversion panel. The binder ispreferably employed in an amount of 1 to 20 parts by mass, morepreferably in an amount of 2 to 10 parts by mass based on the phosphor.

Examples of the organic solvents used for preparing the applicationliquid of the photostimulable phosphor layer include lower alcohols suchas methanol, ethanol, isopropanol and n-butanol; ketones such asacetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone;esters of a lower fatty acid and a lower alcohol such as methyl acetate,ethyl acetate and n-butyl acetate; ethers such as dioxane, ethyleneglycol monoethyl ether and ethylene glycol monomethyl ether; aromaticcompounds such as tolyol and xylol; halogenated hydrocarbons such asmethylene chloride and ethylene chloride; and a mixture thereof.

In addition, there may be incorporated, in the application liquid,various additives, such as a dispersing agent for improving thedispersibility of the phosphor in the application liquid and aplasticizer for enhancing the bonding strength between the binder andthe phosphor in the photostimulable phosphor layer after the formation.Examples of the dispersing agent used for such an object includephthalic acid, stearic acid, caproic acid and oleophilic surfactants.Examples of the plasticizer include phosphate esters such as triphenylphosphate, tricresyl phosphate and diphenyl phosphate; phthalate esterssuch as diethyl phthalate, dimethoxyethyl phthalate; glycolic acidesters such as ethylphthalylethyl glycolate and butylphthalylbutylglycolate; and polyesters of polyethylene glycol and aliphatic dibasicacid such as polyester of triethylene glycol and adipic acid, andpolyester of diethylene glycol and succinic acid. In addition, there maybe incorporated, in the application liquid of the photostimulablephosphor layer, a dispersing agent such as stearic acid, phthalic acid,caproic acid and oleophilic surfactants for the purpose of improving thedispersibility of the photostimulable phosphor particles.

The application liquid of the photostimulable phosphor layer can beprepared by using a dispersing apparatus, such as a ball mill, beadsmill, sand mill, attritor, three-roll mill, high-speed impellerdispersing machine, Kady mill or ultrasonic homogenizer.

The application liquid as prepared above is uniformly coated on thesurface of the support described later to form a coated film. Theapplication can be carried out by conventional applicating means, suchas doctor blade, roll coater, knife coater, comma coater, or lip coater.

Subsequently, the coated film formed by the above means is heated anddried to complete formation of the photostimulable phosphor layer on thesupport. The film thickness of the photostimulable phosphor layer variesdepending on characteristics of the objective radiographic imageconversion panel, the kind of photostimulable phosphors and the mixingratio of the binder to the phosphor, however, in the present invention,it is preferably 0.5 μm to 1 mm, more preferably 10 to 500 μm.

Further, the photostimulable phosphor layer of the present invention mayalso have a protective layer.

This protective layer may be formed by directly applying a protectivelayer application liquid to the photostimulable phosphor layer, or maybe provided by adhering on the photostimulable phosphor layer aprotective layer previously separately formed, or may be provided byforming the photostimulable phosphor layer on a protective layerseparately formed.

As materials for the protective layer, protective layer materials suchas cellulose acetate, nitrocellulose, polymethyl methacrylate, polyvinylbutyral, polyvinyl formal, polycarbonates, polyesters, polyethyleneterephthalate, polyethylene, polyvinylidene chloride, nylons,polytetrafluoroethylene, poly(trifluorochloroethylene),poly(tetrafluoroethylene)-hexafluoro propylene copolymer, vinylidenechloride-vinyl chloride copolymer, and vinylidene chloride-acrylonitrilecoplymer, are commonly used. In addition thereto, a transparent glasssubstrate may also be used as the protective layer.

Furthermore, the protective layer may be formed by depositing inorganicsubstances such as SiC, SiO₂, SiN and Al₂O₃ by use of the vapordeposition method, the sputtering method, etc.

The layer thickness of these protective layers is preferably from 0.1 to2000 μm.

FIG. 3 is a schematic view showing one example of the construction ofthe radiographic image conversion panel of the present invention.

In FIG. 3, the numeral 21 is a radiation generator, 22 is a subject, 23is a radiographic image conversion panel having a visible light orinfrared light photostimulable phosphor layer containing aphotostimulable phosphor, 24 is a photostimulated excitation lightsource for discharging a radiographic latent image of the radiographicimage conversion panel 23 as photostimulated luminescence, 25 is aphotoelectric conversion device for detecting the photostimulatedluminescence discharged by the radiographic image conversion panel 23,26 is an image processing device for reproducing the photoelectricconversion signal detected by the photoelectric conversion device 25 asan image, 27 is an image display device for displaying the reproducedimage, and 28 is a filter for transmitting only the light discharged bythe radiographic image conversion panel 23.

In addition, FIG. 3 is an example of the case of obtaining aradiographic transmitted image of the subject 22. However, when thesubject 22 itself emits radioactive rays, the radiation generator 21 isnot required particularly.

Further, from the photoelectric conversion device 25, they are notlimited to the above if it is possible to somehow reproduce opticalinformation from the radiographic image conversion panel 23.

As shown in FIG. 3, when the subject 22 is disposed between theradiation generator 21 and the radiographic image conversion panel 23,and a radioactive ray R is irradiated, the radioactive ray R transmitsthrough the subject 22 in accordance with changes of radiationtransmittance, and its transmitted image RI (that is, an image ofstrength and weakness of radioactive ray) incidents into theradiographic image conversion panel 23.

The incident transmitted image RI is absorbed to the photostimulablephosphor layer of the radiographic image conversion panel 23, andthereby, electrons and/or positive holes whose number is proportional tothe radiation dose absorbed in the photostimulable phosphor layer aregenerated, and these are accumulated at the trap level of thephotostimulable phosphor.

That is, a latent image accumulating energy of the radiographictransmitted image is formed. Next, the latent image is excited withlight energy and is actualized.

Further, the electrons and/or positive holes accumulated at the traplevel are removed by irradiating a light in visible or infrared regionto the photostimulable phosphor layer according to the light source 24,and the accumulated energy is discharged as photostimulatedluminescence.

The strength and weakness of the discharged photostimulated luminescenceare proportional to the number of the accumulated electrons and/orpositive holes and the strength and weakness of the radiation energyabsorbed in the photostimulable phosphor layer of the radiographic imageconversion panel 23. This optical signal is, for example, converted intoan electronic signal by the photoelectric conversion device 25 such asphotomultiplier or the like, reproduced as an image by the imageprocessing device 26, and the image is displayed by the image displaydevice 27.

It becomes more effective if the image processing device 26 which canonly reproduce the electronic signal as an image signal, but also canperform so-called image processing, arithmetic of image, storing andsaving of image, and the like is used.

Further, when exciting the optical energy, it is required to separatethe reflected light of the photostimulated excitation light and thephotostimulated luminescence discharged from the photostimulablephosphor layer, and the sensitivity of a photoelectric conversion device25, which receives luminescence discharged from the photostimulablephosphor layer, in response to the optical energy generally having shortwavelength of not more than 600 nm becomes high. From these reasons, thephotostimulated luminescence emitted from the photostimulable phosphorlayer is desirable to have a spectrum distribution in a short wavelengthregion.

The luminescence wavelength band of the photostimulable phosphoraccording to the first embodiment of the present invention is between300 nm and 500 nm, on the other hand, the photostimulated excitationwavelength band is between 500 nm and 900 nm, so that it satisfies theabove-described conditions. However, recently, miniaturization ofdiagnostic apparatus proceeds, and a semiconductor laser whoseexcitation wavelength used for reading images of a radiographic imageconversion panel is high power and which is easy to be downsized ispreferable. The wavelength of the semiconductor laser is 680 nm, and thephotostimulable phosphor incorporated in the radiographic imageconversion panel of the present invention shows extremely good sharpnesswhen an excitation wavelength of 680 nm is used.

That is, the photostimulable phosphors according to the first embodimentof the present invention show luminescence having a main peak of notmore than 500 nm, is easy to separate the photostimulated excitationlight, and moreover, corresponds well with the spectral sensitivity of areceiver. Therefore, it can receive lights effectively, and as a result,the sensitivity of an image reception system can be solidified.

As the photostimulated excitation light source 24, a light sourceincluding the photostimulated excitation wavelength of thephotostimulable phosphor used in the radiographic image conversion panel23 is used. Particularly, since the optical system becomes simple when alaser beam is used, and further, the photostimulated excitation lightintensity can be made large, the photostimulated luminescence efficiencycan be improved, so that further preferable results can be obtained.

As a laser, there are metal lasers and the like, such as He—Ne laser,He—Cd laser, Ar ion laser, Kr ion laser, N₂ laser, YAG laser and itssecond harmonic, ruby laser, semiconductor laser, various dye laser,copper vapor laser and the like. Usually, a continuous oscillation lasersuch as He—Ne laser, Ar ion laser or the like is desirable. However, apulse oscillation laser can be used if the scanning time of one pixel ofthe panel is synchronized with the pulse.

Further, when the lights are separated by utilizing delay ofluminescence without using the filter 28, as disclosed in JapanesePatent Laid-Open Publication No. Sho 59-22046, it is preferable to use apulse oscillation laser rather than modulating by using a continuousoscillation laser.

Among the above-described various laser light sources, the semiconductorlaser is small and cheap, and moreover, no modulator is required.Therefore, it is preferable to be used particularly.

As the filter 28, since it is for transmitting the photostimulatedluminescence emitted from the radiographic image conversion panel 23 andfor cutting the photostimulated excitation light, this is determinedaccording to combination of the photostimulated luminescence wavelengthof the photostimulable phosphor contained in the radiographic imageconversion panel 23 and the wavelength of the photostimulated excitationlight source 24.

For example, in case of combination preferable in practical use suchthat the photostimulated excitation wavelength is between 500 nm and 900nm and the photostimulated luminescence wavelength is between 300 nm and500 nm, a purple to blue glass filter such as C-39, C-40, V-40, V-42 orV-44 produced by Toshiba Corporation, 7-54 or 7-59 produced by CorningCorporation, BG-1, BG-3, BG-25, BG-37 or BG-38 produced by SpectrofilmCorporation, or the like can be used. Further, in case of using aninterference filter, a filter having arbitrary properties can beselected and used to some extent. As the photoelectric conversion device25, it may be anything if it is possible to convert changes of amount oflight into changes of electronic signal, such as photoelectric tube,photomultiplier, photodiode, phototransistor, solar battery,photoconductive element and the like.

Second Embodiment

Next, the second embodiment of the radiographic image conversion panelaccording to the present invention will be explained.

The radiographic image conversion panel according to the secondembodiment, contains a photostimulable phosphor obtained by thepredetermined method for manufacturing a radiographic image conversionpanel. In the photostimulable phosphor, a main peak is shown from a(400) face in accordance with X-ray diffraction.

As a result of various investigations, the inventors have found that aphosphor in which a main peak is shown from the (400) face, is improvedin luminance and reduced in afterglow, resulting in improvement in theemission properties of the phosphor.

By showing the main peak from the (400) face, it is presumed that invapor deposition crystals, the transparency of columnar particles isincreased, the luminance is improved and the crystal structure increasedin stability of crystallinity (between lattices) is formed, resulting inimprovement in the afterglow properties.

The photostimulable phosphor layer contains a photostimulable phosphorusing an alkali halide represented by the above-described generalformula (1) as a ground material. The preferable thicknesses of thephotostimulable phosphor layer vary according to the intended use of thephotostimulable phosphor or according to types of photostimulablephosphor. From the viewpoint of obtaining the effect of the presentinvention, the thickness thereof is 50 μm to 20 mm, preferably 50 μm to1 mm, more preferably 50 to 300 μm, still more preferably 100 to 300 μm,and particularly preferably 150 to 300 μm.

As the photostimulable phosphor which can be used in the phosphor layerto be applied, similarly to the first embodiment, the photostimulablephosphor exhibiting a stimulated fluorescence having a wavelength of 300to 500 nm by an excitation light having a wavelength of 400 to 900 nm iscommonly used.

The photostimulable phosphor is manufactured by heating the samephosphor raw materials as the first embodiment in a vacuum. The heatingtemperature is at 400° C. or more. As phosphor materials of thephotostimulable phosphor, the compounds described in (a) to (c) of thefirst embodiment are used. However, in the second embodiment, inaddition, the activator may added to the phosphor materials. As a rawmaterial of the activator, a compound including at least one metal atomselected from Eu, Tb, In, Cs, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu,Sm, Y, Tl, Na, Ag, Cu, Mg and the like, is used.

Next, the photostimulable phosphor layer of the present invention ismanufactured by the above-described vapor phase growth method. As anevaporation source, the source prepared by adding Rb atoms so that aratio of Rb atoms to Cs atoms is finally 5/1,000 mol or lower,preferably 1/1,000,000 to 5/1,000 mol, is used. By preparing theevaporation source at the ratio, the phosphor in which the main peak isshown from the (400) face, can be obtained. The vapor phase growthmethod can be performed in a vacuum, in an inert gas atmosphere, in aH₂/N₂ mixed gas atmosphere.

The photostimulable phosphor layer according to the second embodimentcan be manufactured by a manufacturing method in which theabove-described application method is adopted. The photostimulablephosphor layer is mainly made from a phosphor and a polymer resin. Thephotostimulable phosphor layer is formed by applying it to a supportwith a coater. The manufacturing method is the same as that of the firstembodiment except the following matters.

In particular, in order to grow the phosphor in which the main peak isshown from the (400) face, the photostimulable phosphor applicationliquid is prepared by adding Rb atoms to a photostimulable phosphor ofthe photostimulable phosphor layer so that a ratio of the Rb atoms to Csatoms is 5/1,000 mol or lower, preferably 1/1,000,000 to 5/1,000 mol. Inthe method for preparing the photostimulable phosphor applicationliquid, as a solvent, for example, one of the solvents explained in thefirst embodiment is used.

In the application liquid as a liquid phase including Cs atoms, after apredetermined liquid membrane phase is sequentially formed, the organicsolvent having a solubility different from that of the applicationliquid is added under stirring. Then, the photostimulable phosphorprecursor is obtained.

By calcining the obtained phosphor precursor at 600 to 800° C., aphotostimulable phosphor is obtained.

EXAMPLES

The present invention is described in detail below by referring to theExamples, however, the embodiments of the present invention are notlimited to these Examples.

Example 1

[Preparation of Radiographic Image Conversion Panel Samples A1 to A10]

According to the conditions shown in Table 1, a photostimulable phosphorlayer having a photostimulable phosphor (CsBr:Eu) was formed on thesurface of a support of glass ceramics (produced by Nippon ElectricGlass Co., Ltd.) having a thickness of 1 mm by using a depositionapparatus (wherein θ1 and θ2 are set to θ1=5° and θ2=5°) shown in FIG.4.

In the deposition apparatus shown in FIG. 4, the distance d between thesupport and an evaporation source was made to be 60 cm. Then, by using aslit made of aluminum, deposition was performed by carrying the supporttoward the direction parallel to the longitudinal direction of the slitso as to obtain a photostimulable phosphor layer having a thickness of300 μm.

In the vapor deposition, the support was placed in the vapor depositionapparatus, 1 mol of CsBr:Eu was then placed in every 1/4 mol portion oneach of four boats to prepare a first evaporation source. Then, EuBr₂ asa second evaporation source was divided into two boats to give the Euamount ratio shown in Table 1, and the evaporation sources 1 and 2 werepress-molded and fed into a water-cooled crucible.

Thereafter, the air inside of the deposition apparatus 1 was discharged,and N₂ gas was introduced. After the degree of vacuum was adjusted to0.133 Pa, the vapor deposition was performed under the conditions wherethe temperature of the first and second evaporation sources was 700° C.and the deposition rate of each source was 10 μm/min. The vapordeposition was completed when the film thickness of the photostimulablephosphor layer was 300 μm. Subsequently, the phosphor layer wassubjected to a heat treatment at a temperature of 400° C. In anatmosphere of dried air, the support and the peripheral portion of aprotective layer having a borosilicate glass were sealed by an adhesiveto obtain the radiographic image conversion panel sample A-1 (sampleA-1) having a construction where the phosphor layer was sealed.

Next, in Example 1, the radiographic image conversion panel samples A-2to A-10 were prepared (samples A-2 to A-10) in the same manner as inExample 1, except for using the evaporation sources 1 and 2 as shown inTable 1 and giving the Eu amount ratio as shown in Table 1.

The respective radiographic image conversion panels (samples A-1 toA-10) prepared were evaluated as follows.

[Evaluation of Luminance]

The luminance was evaluated by using the Regius 350 produced by KonicaCorporation.

[Evaluation Method and Evaluation Criteria of Durability]

Durability was evaluated under the conditions of 30° C. and 80% in astate where a vapor deposition film formed on the substrate (support)was not sealed.

As the evaluation of durability, there was measured the time which theluminance takes to decrease to 80% of the initial value.

Further, the ratio between the Eu amount in the front end of thephotostimulable phosphor crystal and the Eu amount in the vicinity ofthe support (the amount ratio of Eu) was determined by the methoddescribed above in detail.

Further, a mean crystal size (a mean value of 10 phosphor crystals) wasmeasured by XRD and calculated using the Scherrer's method. TABLE 1 MeanFirst Second Eu Crystal Evaporation Evaporation Amount Size SampleSource Source Ratio (nm) Luminance Durability Remarks A-1 CsBr EuBr² 0.995 1.34 30 days Present element element Invention 1 A-2 CsBr:Eu EuBr²0.9 99 1.22 28 days Present element Invention 2 A-3 CsBr:Eu CsBr:Eu 0.9105 1.88 45 days Present Invention 3 A-4 CsBr:Eu CsBr:Eu 0.8 101 1.86 60days Present Invention 4 A-5 CsBr:Eu CsBr:Eu 0.7 110 1.77 80 daysPresent Invention 5 A-6 CsBr:Eu CsBr:Eu 0.6 106 1.78 90 days PresentInvention 6 A-7 CsBr:Eu CsBr:Eu 0.5 108 1.66 100 days Present Invention7 A-8 CsBr:Eu — 1 85 0.21 2 hours Comparative Example 1 A-9 CsBr:Eu —1.1 83 0.02 30 minutes Comparative Example 2 A-10 CsBr:Eu — 1.2 80 0.0110 minutes Comparative Example 3

As is apparent from Table 1, it is found that the samples of the presentinvention are excellent as compared with those of Comparative Examples.

Example 2

[Preparation of Radiographic Image Conversion Panel Samples B1 to B10]

(Method for Forming Phosphor Particles—Prepared by Deposition)

According to the conditions shown in Table 2, a photostimulable phosphorlayer having a photostimulable phosphor (CsBr:Eu) was formed on thesurface of a support of glass ceramics (produced by Nippon ElectricGlass Co., Ltd.) having a thickness of 1 mm by using a depositionapparatus (wherein θ1 and θ2 are set to θ1=5° and θ2=5°) shown in FIG.4.

In the deposition apparatus shown in FIG. 4, the distance d between thesupport and an evaporation source was made to be 60 cm. Then, by using aslit made of aluminum, deposition was performed by carrying the supporttoward the direction parallel to the longitudinal direction of the slitso as to obtain a photostimulable phosphor layer having a thickness of300 μm.

In the vapor deposition, the support was placed in the vapor depositionapparatus, Rb in an amount described in Table 1 was added to phosphorraw materials (CsBr: Eu) and the resulting mixture was fed into awater-cooled crucible after being shaped using a press as a evaporationsource.

As a result of the X-ray analysis, there was obtained a phosphor inwhich a main peak is shown from a (400) face.

Subsequently, the vapor deposition apparatus was once degassed and thenan N₂ gas was introduced thereinto to adjust a degree of vacuum to1×10⁻¹ Pa. Thereafter, the vapor deposition was carried out whilemaintaining a temperature of the support (also referred to as asubstrate temperature) at about 150° C. The vapor deposition wascompleted when the film thickness of the photostimulable phosphor layerwas 300 μm.

The support having provided thereon the photostimulable phosphor layerwas placed and sealed in a barrier bag (GL-AE, produced by ToppanPrinting Co., Ltd.) of which the rear surface was stuck with an AL foil,whereby a radiographic image conversion panel sample B-1 was prepared.

The samples B-2 to B-6 were obtained in the same manner as in sampleB-1, except for changing the added amount of Rb, and the heatingtemperature and atmosphere for forming phosphors.

In the phosphors of the samples B-2, B-3, B-5 and B-6, a main peak isshown from the (400) face.

(Phosphor Layer—Prepared by Application)

CsCO₃, HBr and Eu₂O₃ were mixed so that the amount of Eu was 5/10000 molper 1 mol of CsBr, followed by dissolving. Further, Rb was added theretoin an amount described in Table 2. The aqueous solution was condensed at90 to 110° C. to prepare a saturated solution, thereby serving this asan aqueous solution liquid phase.

On the liquid phase, an EDTA liquid film forming layer and a phasecomprising isopropyl alcohol are sequentially formed. This liquid wasstirred at 3000 rpm by a homogenizer to result in precipitation ofspherical CsBr particles and thereby obtaining a CsBr:Er phosphorprecursor with a size of 5 micron.

The ratio between the aqueous phase and the organic phase was 1:1.

The phosphor precursor was subjected to calcination at 620° C. for 2hours in a vacuum atmosphere to form a phosphor particle.

For forming a phosphor layer, the phosphor particle and a polyestersolution (BYRON 63 ss, produced by Toyobo Co., Ltd.) were mixed anddispersed as a resin solution having a solid content concentration of95% by mass and a phosphor concentration of 5% by mass to prepare acoating material.

On the surface of a polyethylene terephthalate film (size: 188×30,produced by Toray Industries, Inc.) support with a size of 188 micron,this application material was coated and dried in a drying zonecomprising three zones of 80° C., 100° C. and 110° C. in an Ar inertoven under a drying atmosphere at a rate of CS: 2 m/min to form aphotostimulable phosphor layer.

A sheet having formed thereon the photostimulable phosphor layer wasplaced and sealed in a barrier bag (GL-AE, produced by Toppan PrintingCo., Ltd.) of which the rear surface was stuck with an AL foil, wherebya radiographic image conversion panel (sample B-7) was prepared.

The samples B-8 to B-10 were prepared in the same manner as in sampleB-7, except for changing the added amount of Rb, and the heatingtemperature and atmosphere for forming phosphor particles as shown inTable 2.

In the phosphors of the samples B-7 and B-8, a main peak is shown fromthe (400) face.

Each sample was subjected to the following evaluations.

[Evaluation of Sharpness]

The sharpness of respective radiographic image conversion panel samplesprepared was evaluated by determining a modulation transfer function(MTF).

The MTF was determined by a method where a CTF chart was attached toeach radiographic image conversion panel sample, each sample was thenirradiated with an X-ray of 80 kVp in an amount of 10 mR (a distance tothe object: 1.5 m), and the CTF chart image was scanned and read out byuse of a semiconductor laser (Wavelength: 680 nm, Power at the surfaceof panel: 40 mW) with a diameter of 100 μmφ. Values in Table are shownby a summation of MTF values at 2.0 lp/mm. The results obtained areshown in Table 2.

[Evaluation of Luminance]

The luminance was evaluated by using the Regius 350 produced by KonicaCorporation.

In the same manner as in the evaluation of sharpness, an X-ray wasirradiated at a distance between the radiation source and the plate of 2m by use of a tungsten vessel at a tube voltage of 80 kVp and a tubecurrent of 10 mA. Thereafter, emitted light was read out by use ofRegius 350 provided with a plate. The evaluation was performed based onthe obtained electric signals from a photomultiplier.

The photographed in-plane electric signal distributions obtained fromthe photomultiplier, were comparatively evaluated to determine standarddeviations which were designated as luminance distributions of eachsample (S. D.). As the value is smaller, the luminance unevenness ismore reduced.

[Evaluation of Afterglow]

Each sample was cut into a square of 50 mm, affixed to a plate and setinto a radiographic cassette.

When X-rays are irradiated and the radiographic image is read, thesignal difference from the 50th picture element is designated as anafterglow value. In Table, the temperature expresses a heatingtemperature of respective phosphor fine particles. TABLE 2 Added Amountof Rb Heating (400) Luminance (mol/Cs Temperature Face MTF UnevennessSample 1 mol) (° C.) Atmosphere Ratio Luminance (2 lp/mm) (S.D.)Afterglow B-1 5/100000 600 vacuum 2:1 1.67 32% 4 0.00004 B-2 5/10000 600vacuum 4:1 1.72 33% 8 0.00002 B-3 5/1000 600 vacuum 3:1 1.54 31% 100.00003 B-4 1/100 600 vacuum 1:2 0.43 11% 43 0.00002 B-5 5/10000 600 Ar3:1 1.22 32% 9 0.00005 B-6 5/10000 600 H₂/N₂ 3:1 1.18 34% 8 0.00004 B-75/10000 600 vacuum 4:1 1.52 31% 3 0.00001 B-8 5/10000 600 vacuum 4:11.55 35% 4 0.00008 B-9 0 0.12 12% 56 0.00321 B-10 0 0.10 10% 44 0.00582

In Table 2,

1. samples B-1 to B-3, B-5 and B-6 (present invention), sample B-4(comparative example) vapor deposition type

2. samples B-7 and B-8 (present invention), samples B-9 and B-10(comparative example) application type

As can be seen from Table 2, the samples according to the presentinvention are excellent as compared with comparative samples.

The radiographic image conversion panel and the method for manufacturingthe radiographic image conversion panel according to the presentinvention ensure high luminance and high sharpness, and have anexcellent effect also on durability.

The radiographic image conversation panel and method for manufacturing aphosphor according to the present invention are reduced in afterglow andhas an excellent effect on luminance and sharpness despite the low cost.

While the preferred embodiments of the present invention have beendescribed using specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the appendedclaims.

1. A radiographic image conversion panel comprising: a support; and atleast one photostimulable phosphor layer provided on the support,wherein at least one layer of the photostimulable phosphor layerscontains a photostimulable phosphor using an alkali halide representedby a following general formula (1) as a ground material, and thephotostimulable phosphor layer is formed so as to have a thickness from50 μm to 20 mm by a vapor phase growth method, and a mean crystal sizein the photostimulable phosphor of the photostimulable phosphor layer isfrom 90 to 1000 nm, and the general formula (1) is expressed byM ¹ X·aM ² X′ ₂ ·bM ³ X″ ₃ :eA  (1) wherein the M¹ is at least one kindof alkali metal selected from a group consisting of Li, Na, K, Rb andCs, the M² is at least one kind of bivalent metal atom selected from agroup consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu and Ni, the M³ is atleast one kind of trivalent metal atom selected from a group consistingof Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu,Al, Ga and In, each of the X, the X′ and the X″ is at least one kind ofhalogen selected from a group consisting of F, Cl, Br and I, the A is atleast one kind of metal atom selected from a group consisting of Eu, Tb,In, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, Ti, Na, Ag, Cu and Mgand each of the a, the b and the e represents a numeric value in a rangeof 0≦a<0.5, 0≦b<0.5 and 0<e≦0.2.
 2. The radiographic image conversionpanel of claim 1, wherein the photostimulable phosphor is CsBr:Eu.
 3. Amethod for manufacturing the radiographic image conversion panel ofclaim 1, comprising controlling a deposition rate of a main agent of thephotostimulable phosphor and a deposition rate of an activator of thephotostimulable phosphor by at least two or more systems.
 4. A methodfor manufacturing a radiographic image conversion panel comprising asupport and a photostimulable phosphor layer provided on the support;the method comprising adding Rb atoms to a photostimulable phosphor ofthe photostimulable phosphor layer so that a ratio of the Rb atoms to Csatoms is 1/1,000,000 to 5/1,000 mol.
 5. A radiographic image conversionpanel comprising a photostimulable phosphor obtained by the method formanufacturing the radiographic image conversion panel of claim 4,wherein in the photostimulable phosphor, a main peak is shown from a(400) face in accordance with a result of X-ray diffraction.
 6. Theradiographic image conversion panel of claim 5, comprising: aphotostimulable phosphor layer, wherein the photostimulable phosphorlayers contains the photostimulable phosphor using an alkali haliderepresented by a following general formula (1) as a ground material, thephotostimulable phosphor layer is formed by spherical phosphor particlesand a polymer material, the photostimulable phosphor layer is formed soas to have a thickness from 50 μm to 20 mm, the general formula (1) isexpressed byM ¹ X·aM ² X′ ₂ ·bM ³ X″ ₃ :eA  (1) wherein the M¹ is at least one kindof alkali metal selected from a group consisting of Li, Na, K, Rb andCs, the M² is at least one kind of bivalent metal atom selected from agroup consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu and Ni, the M³ is atleast one kind of trivalent metal atom selected from a group consistingof Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu,Al, Ga and In, each of the X, the X′ and the X″ is at least one kind ofhalogen selected from a group consisting of F, Cl, Br and I, the A is atleast one kind of metal atom selected from a group consisting of Eu, Tb,In, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, Ti, Na, Ag, Cu and Mgand each of the a, the b and the e represents a numeric value in a rangeof 0≦a<0.5, 0≦b<0.5 and 0<e≦0.2.
 7. The radiographic image conversionpanel of claim 5, wherein phosphor fine particles in the photostimulablephosphor are formed by heating at 400° C. or more.
 8. A photostimulablephosphor precursor, wherein phosphor particles in the radiographic imageconversion panel of claim 5 are formed in a vacuum.
 9. A method forforming the photostimulable phosphor precursor of claim 8, comprising:sequentially forming a liquid membrane phase in a liquid phasecontaining Cs atoms, and adding an organic solvent having a solubilitydifferent from that of the liquid phase containing Cs atoms understirring.
 10. A photostimulable phosphor obtained by calcining thephosphor precursor of claim 8 at 600 to 800° C.